Thermodynamic cycle heat engines (hereinafter referred to as engines or heat engines) apply the principles of heat regeneration and thermodynamic cycles to provide the power for the engine. These engines can be adapted to implement a number of thermodynamic cycles including the Stirling cycle. An engine employing the Stirling cycle (hereinafter referred to as a Stirling engine) includes a high temperature or expansion chamber and a low temperature or compression chamber. To increase efficiency, a regenerator also is added. A working fluid expands in the hot chamber, due to heat applied to the chamber, and force is applied to a piston in the chamber by the expanding fluid. The heated fluid is forced from the high temperature chamber to the low temperature chamber through the regenerator, which absorbs portions of the heat contained in the working fluid. The cooled fluid, which can be further cooled in a heat exchanger, is returned to the high temperature chamber through the regenerator. The cooled fluid absorbs heat from the regenerator. The working fluid is then reheated to repeat the cycle.
A multi-cylinder Stirling engine (MSE) is described in U.S. Pat. No. 4,392,351. The MSE includes a bi-directional regenerator and a Stirling engine as described in U.S. Pat. No. 3,985,110. Unfortunately, the two paths through the regenerator have essentially the same volume and cross-sectional configuration as shown in FIG. 3. However, the optimal volume and configuration for these paths are quite different. For the fluid from the high temperature chamber to the low temperature chamber, a slower velocity is optimal to enable greater heat transfer. Also, it is beneficial to minimize compression of the fluid in the regenerator. Thus, a large volume is desired for the path. Also, fins and other protuberances that slow fluid velocity are desirable. However, for the fluid from the low temperature chamber to the high temperature chamber, the optimal conditions are nearly opposite. That is, it is advantageous to minimize the volume of the path to increase the pressure of the working fluid as it moves through the path, which increases the overall efficiency of the engine. Further, the regenerator for the MSE is external to the Stirling engine, requiring extra space, piping, and fittings.
The MSE also uses a pair of fixed and movable plates to control the phasing of the thermodynamic cycles. Unfortunately, these plates add to the size, weight, complexity, and cost of the engine. Further, the plates limit the surface area of the low and high temperature chambers that is in contact with the heat and cold sources necessary to motivate the Stirling cycle. For example, the ends of the chambers are essentially blocked by the respective plates. To make up for this loss of heat transfer capability, heat exchangers are used. Unfortunately, the exchangers decrease the efficiency and increase the size, complexity, and cost of the MSE.
The MSE attaches rotor lobes to exterior walls of chambers and rotates the chambers to affect movement of the attached rotors. Unfortunately, the rotation of the chambers further limits the direct exposure of the chambers to the cold and heat sources needed to power the Stirling cycle and can lead to seal problems.
A rotary Stirling engine (RSE) is described in U.S. Pat. No. 5,335,497. The efficiency of a heat engine is directly related to the change in pressure for the working fluid during the thermodynamic cycle. Unfortunately, the RSE does not isolate the hot and cold chambers. Thus, the compression of the working fluid occurs in the heat exchangers as well as the chambers, which decreases the efficiency of the engine. Also, the heat transfer between the working fluid and the heat exchangers is limited, since the working fluid is not allowed to remain at rest in the exchangers during the cycles. Further, the external heat exchangers and associated piping add to the size, complexity, and cost of the engine. Also, no more than two volumes can be created in each chamber, limiting the number of thermodynamic cycles that can be completed by one revolution of the rotors in the chambers.
A rotary engine (RE) using separate compressor and combustion chambers is described in U.S. Pat. No. 4,901,694. Each chamber includes a single rotor with two lobes. Unfortunately, using only one rotor per chamber limits the number of cycles that can be completed per rotation of the rotors. The gear train for the RE also is complex. For example, to move each rotor through one cycle per rotation, a sequence of four elliptical gears is used. Further, the gear train is one-sided, which results in vibration problems.
What is needed is a thermodynamic cycle heat engine with isolated compression, transfer, and expansion cycles and optimized regeneration of the working fluid. Further, a means for increasing the number of thermodynamic cycles associated with each revolution of rotors in the chambers and an efficient gear train for controlling the rotors and cycles are needed. Also, it would be desirable to reduce the complexity of the engine and enable a greater exposure of the high temperature chamber and low temperature chambers to the respective thermal sources.